It is a well-known fact that arteriosclerosis is an extremely important factor causing various circulatory diseases, and active studies have been undertaken in an attempt to achieve suppression of the evolution of arterial sclerosis or regression thereof. In particular, although the usefulness of a pharmaceutical agent which reduces cholesterol in blood or arterial walls has been acknowledged, an ideal pharmaceutical agent exhibiting positive clinical effects while causing less side-effects has not been realized. A pharmaceutical agent which directly inhibits deposition of cholesterol in arterial walls has been desired as a pharmaceutical agent which effectively prevents or treats arterial sclerosis, and studies in this field are thriving. Yet, an ideal pharmaceutical agent has not been developed.
In recent years, it has been clarified that cholesterol in blood is accumulated in arterial walls in the ester form thereof, and that it significantly evolves arteriosclerosis. A decrease in cholesterol level in blood leads to the reduction of accumulation of cholesterol ester in arterial walls, and is effective for the suppression of evolution of arteriosclerosis and regression thereof.
Cholesterol in food is esterified in mucous membrane of small intestine, and taken into blood as chylomicron. ACAT is known to play an important role in the generation of cholesterol ester in mucous membrane of small intestine. Thus, if esterification of cholesterol can be suppressed by inhibiting ACAT in mucous membrane of small intestine, absorption of cholesterol by mucous membrane and into blood can be presumably prevented to ultimately result in lower cholesterol level in blood.
In arterial walls, ACAT esterifies cholesterol and causes accumulation of cholesterol ester. Inhibition of ACAT in arterial walls is expected to effectively suppress accumulation of cholesterol ester.
From the foregoing, it is concluded that an ACAT inhibitor will make an effective pharmaceutical agent for hyperlipemia and arteriosclerosis, as a result of suppression of absorption of cholesterol in small intestine and accumulation of cholesterol in arterial walls.
Conventionally, there have been reported, for example, as such ACAT inhibitors, amide and urea derivatives [J. Med. Chem., 29: 1131 (1986), Japanese Patent Unexamined Publication Nos. 117651/1990, 7259/1990, 234839/1992, 327564/1992 and 32666/1993]. However, creation and pharmacological studies of these compounds have been far from sufficient.
Meanwhile, hyperoxidation of low density lipoprotein (LDL) is also highly responsible for intracellular incorporation of cholesterol accumulated as cholesterol ester in arterial walls. In addition, it is known that hyperoxidation of lipids in a living body is deeply concerned with the onset of arteriosclerosis and cerebrovascular and cardiovascular ischemic diseases.
Accordingly, a compound having both an ACAT inhibitory activity and lipoperoxidation inhibitory activity is highly useful as a pharmaceutical product, since it effectively reduces accumulation of cholesterol ester in arterial walls and inhibits lipoperoxidation in living organisms, thereby preventing and treating various vascular diseases caused thereby.
It is therefore an object of the present invention to provide a compound having ACAT inhibitory activity and lipoperoxidation inhibitory activity, as well as pharmaceutical use thereof, particularly ACAT inhibitor and lipoperoxidation inhibitor.